1. Field of the Invention
The invention relates to a slicer utilized in an optical disc drive, and more particularly, to a slicer capable of dynamically adjusting slice level according to a wobble signal read from a DVD-R/RW optical disc.
2. Description of the Prior Art
In present day information society, storage of large amounts of information has become a major problem. Of all types of storage medium, the optical disc is one of the most useful mediums because of its high storage capacity and small physical volume. However, as multimedia technology progresses increased storage requirements are required, and the storing capacity of a normal CD optical disc (650 MB) is becoming increasingly less satisfactory. Therefore, a new optical disc standard, the digital versatile disc (DVD), with increased storage capacity, has emerged. The physical size of a DVD is almost identical to that of a CD; however, the storage capacity of a DVD is much larger than that of a CD. However, because the CD-R and CD-RW discs can easily stores needed data, similarly, the standards of the DVD-R disc and the DVD-RW disc are created so that users can utilize DVD-R or DVD-RW discs much like the CD-R and CD-RW discs to store an increased amount of data.
As done with the CD disc, a specific structure is installed on a DVD-RW multi-function digital disc for addressing stored data and consequently for easily accessing the data. Please refer to FIG. 1, which is a schematic diagram of a DVD-R/RW multi-function digital disc 10 according to the prior art. The DVD-R/RW multi-function digital disc 10 comprises a substrate 12, a reflective layer 14, and a protective layer 16. Furthermore, a plurality of grooves are set on the surface of the DVD-R/RW multi-function digital disc 10 such that a optical pick-up unit (OPU) output a write-in power according to a write-in ploy for writing a plurality recording marks 20 in the groove 18. Generally speaking, in order to smoothly store recording marks 20 in the correct position of the DVD-R/RW multi-function digital disc 10, the optical disc drive has to know the track information of DVD-R/RW multi-function digital disc 10. Therefore, the DVD-R/RW multi-function digital disc 10 has a wobble track 22 to store the track information. In other words, the optical disc drive can read a wobble signal from the wobble track and then decode the wobble signal to obtain needed track information.
According to the prior art DVD-R standard, the DVD-R/RW multi-function digital disc 10 utilizes a plurality of land pre-pit (LPP) 24a, 24b for modulating the wobble signal to store the track information. Please refer to FIG. 2, which is a diagram of a wobble signal 30 generated by the wobble track 22 shown in FIG. 1. An optical pick-up unit reads the wobble track 22 to generate the wobble signal 30. When the optical pick-up unit moves to the LPP 24a, the optical pick-up unit is affected by the LPP 24a so that the optical pick-up unit suddenly generates a spike 32a. Similarly, when the optical pick-up unit moves to the following LPP 24b, the optical pick-up unit generates a spike 32b, too. Therefore, the LPPs 24a, 24b can be pre-installed on the DVD multi-function digital disc 10 for forming the wobble signal 30. In other words in the prior art, the DVD multi-function digital disc 10 utilizes different LPPs having different positions for driving the wobble signal 30 to generate spikes to store the track information. Therefore, the optical disc drive at last needs to detect the spikes 32a, 32b to determine stored data in the wobble signal. As known by those skilled in the art, the wobble signal 30 actually does not have the ideal waveform shown in FIG. 2. That is, signal amplitude of the wobble signal 30 changes, and different DVD multi-function digital discs 10 have different wobble signals 30. Therefore, when the optical disc drive utilize a data slicer detects the spikes of the wobble signal 30 through a fixed slice level, an error determination may occur so that the following decoding operation of the wobble signal 30 is affected.